Phase and microstructural analysis of novel refractory high entropy alloy Y-doped Al-Hf-Nb-Ti-V system

A new Y-doped Al-Hf-Nb-Ti-V refractory high-entropy alloy (RHEA) system was developed as a candidate material for high-temperature structural applications. Microstructural investigation and X-ray diffraction (XRD) characterization results indicated that the as-cast alloy exhibits a non-homogeneous microstructure with distinct dendritic and interdendritic regions. The addition of the equimolar ratio of Al to the HfNbTiV RHEA resulted in an amorphous phase and a small amount of intermetallic phase formation. The enthalpy calculation revealed that this alloy has ∆H _mix = -16.2 kJ.mol ⁻¹ and a δ parameter of 5.8%, which are considerably lower and negative for the former and lower for the latter compared with the conventional high entropy alloys. The addition of the minor Y element slightly increases the value of δ and ∆H _mix which suppresses the occurrence of the amorphous phase and contributes to the intermetallic compound formation by increasing the amount of strongly chemically attracted atomic pairs (SCAAPs) Al-Hf and Al-Y beyond a critical value.